1. Field of the Invention
This invention relates to an XY table which is movable in directions orthogonal to each other.
2. Description of the Prior Art
An XY table is known which has a table movable in one direction and also movable in a direction orthogonal to said one direction and in which an upper table movable in one direction is placed on a lower table movable in one direction so that the directions of movement of the upper and lower tables are orthogonal to each other. In such XY table, a driving motor for the lower table is fixed to a base bed and a motor for driving the upper table and a driving system such as a feed screw are assembled onto the lower table and therefore, the weight loaded onto the lower table becomes great and this has led to a disadvantage that quick stoppage or quick starting of the lower table is difficult due to great inertia.
As an XY table which eliminates such a disadvantage, there is known an XY table in which the driving motor for the upper table is fixed to the base bed similarly to the motor for the lower table.
In this XY table, a guide rail parallel to the direction of movement of the lower table is provided on the upper table, and a moving member movable in the direction of movement of the upper table by the upper table driving motor and the guide rail are slidably coupled together through an antifriction bearing, the upper table being movable in the direction of movement of the lower table by the lower table driving motor and also movable in the direction of movement of the upper table by the upper table driving motor.
In such XY table, the upper table driving motor is fixed to the base bed and therefore, unlike the conventional XY table, the load weight for the lower table can be made small and this is desirable where the table is operated at a high speed.
However, the conventional XY table in which the upper table driving motor is fixed to the base bed has been of such a construction that the coupling between the guide rail of the upper table and a member moved by the upper table driving motor is sandwiched by antifriction bearings respectively fitted to two support shafts fixed to said member and therefore, it has been impossible to adjust the pre-pressure of the antifriction bearings with respect to the guide rail to a predetermined level, and the fact that the support shafts are fixed has led to a disadvantage that pre-pressure leakage or back-lash of the antifriction bearings is liable to occur due to abrasion of the antifriction bearings or the guide rail.
Also, in the conventional coupling portion, the support shafts of the antifriction bearings have been supported in a cantilever fashion and this has led to a disadvantage that with a pre-pressure applied to the antifriction bearings, the support shafts are liable to be bent or damaged.